In the field of rotary sensors that measure the magnetic field direction there are rotary sensors that use a permanent magnet at the tip of a rotating shaft of which position is to be measured and at least two magnetically-sensitive members that measure the magnetic field direction on the rotation axis of the moving shaft. However, these devices exhibit restrictions particularly when it comes up to measuring the rotary displacement of a shaft passing through the sensor itself because, in this case, it is impossible to place the magnetically-sensitive members on the rotation axis of the system. In the case of linear sensors, there are structures that use an axially magnetized disk magnet and at least two magnetically-sensitive members that measure the magnetic field direction but these sensors are limited to linear strokes as low as about 20 mm because the amplitude of both components used for the measurement of the field direction becomes too low when the stroke to be measured rises.
It is known from prior art, patent FR2893410 of the applicant, which uses two components of the magnetic induction, generated by a substantially diametrically magnetized ring magnet, measured in a single and same place located close to the median plan of the magnet. A computation of the arctangent of the ratio of both induction components (radial and tangential component) makes it possible to derive the angular position of the magnet. It is however necessary to apply beforehand a correction factor between these two components, in fact in this sensor, the amplitude of both components of the magnetic induction is substantially different.
Typically, this report varies in the range of 1.5 to 4 but the more the magnet diameter is large the more this ratio increases. The increase of the ratio is mainly due to the reduction in the tangential component. For the large diameter magnets, the amplitude of the tangential component is such that it becomes incompatible with the magnetically sensitive members that are conventionally used for this type of sensor and therefore the measurement of the angular position of the magnet is no longer satisfactorily guaranteed. Likewise, the weak amplitude of the tangential component makes the sensor sensitive to the magnetic disruptions that can apply on the sensor.
This correction factor can also lead to problems of measurement precision and the higher this factor is the greater the mistake will be. Furthermore, the necessity of having an amplification ratio between both components before the computation of the position (arctangent) leads to an incompatibility of these systems with certain types of magnetically sensitive members (e.g.: magneto-resistor). Furthermore, there are solutions of revolutions count, for applications of flywheel angle sensor, based on magneto-resistors as described for example in patent EPI 532425B1 which requires that the ratio between both components be lower than 1.5 and that the amplitudes of both components be close to 200 G.
It is also known from the related art, U.S. Pat. No. 0,208,727 illustrated by FIG. 1a. This document describes a position sensor rotating on 360° and which uses two magnetically sensitive probes A4, A5 that are angularly offset by 90° and 4 ferromagnetic pieces A10 in order to determine the angular position of a substantially diametrically magnetized disc A2 magnet. The two 2 magnetically sensitive members A4, A5, sensitive to the amplitude of the magnetic induction generated by magnet A2, are positioning in the 2 air-gaps defined by the 4 ferromagnetic pieces A10 that allow the equalization of the amplitudes of the ferromagnetic field components. In this structure, the volume of the ferromagnetic pieces is very important and the construction of such a sensor is difficult because it requires a precise positioning of these ferromagnetic pieces A10. This leads to an important manufacturing cost.
It is also known from the related art, patent documents no. US 2002/0179825 and U.S. Pat. No. 5,942,895 describing respectively an angular position magnetic sensor with and a magnetic sensor provided with concentrators arranged to restrict the measurement to one of the components of the measured magnetic field. Meanwhile, the teaching of these documents does not carry out a reliable position detection from a magnet with a magnetization direction that is continuously variable along its displacement direction, nor even to respond to the technical problems that are previously mentioned.